1. Field of the Invention
The present invention is directed to the field of shock absorbers and, more particularly, to a rod guide for use in a monotube shock absorber.
2. Description of the Related Art
Monotube shock absorbers are well-known devices for cushioning machines (such as vehicles) from vibration and sudden jolts. Such monotube shock absorbers are described, for example, in U.S. Pat. No. 6,253,661.
Monotube shock absorbers generally have a piston/cylinder unit in which a piston rod is slidably movable in a straight line along the longitudinal axis of a cylinder. A piston rod guide mounted within the cylinder provides a point of contact between the piston rod and the cylinder as the piston reciprocates within the cylinder. Thus, rod guides must be sufficiently stable and robust to withstand the environment in which they operate, which is often very hot and subject to forces and stresses in varying directions. The rod guides must also be easily slidable along the piston rod (i.e., they must have a low coefficient of friction with the piston rod), and provide a reliable seal to prevent contamination of the interior of the cylinder which could impair operation of the shock absorber.
Many known rod guides, such as those shown in U.S. Pat. No. 6,253,661 and in United States Published Patent Application Publ. No. US2003/0070893, are complicated assemblies with many parts, making them difficult and costly to assemble. In addition, in many such rod guides, the points of contact are formed of metal, such as sheet metal or aluminum with hardcoating, which has a relatively high coefficient of friction, as a result of which these rod guides are less efficient than desired. Many designs require side loads from the piston rod to contact an unlubricated bearing. Although some known rod guides with sheet metal bushings are therefore coated with a material having a lower coefficient of friction, such coatings wear off, leaving the metal bushing in direct contact with the piston rod, and consequent deterioration in performance of the shock absorber.
There is accordingly a need in the art for simple, inexpensive rod guides that provide improved coefficients of friction with respect to the piston rods with which they are used.